Follow the nitrogen to extraterrestrial life

The narrow search for water may miss important clues, say USC geobiologists

The great search for extraterrestrial life has focused on
water at the expense of a crucial element, say
geobiologists at the University of Southern California.

Writing in the Perspectives section of the May 5 issue of
Science, four USC researchers propose searching for
organic nitrogen as a direct indicator of the presence of life.
Nitrogen is essential to the chemistry of living organisms.

Even if NASA were to find water on Mars, its presence only
would indicate the possibility of life, said Kenneth Nealson,
Wrigley Professor of earth sciences in the USC College of
Letters, Arts and Sciences.

"It's hard to imagine life without water, but it's easy to
imagine water without life," Nealson said.

The discovery of nitrogen on the Red Planet would be a
different story.

"If you found nitrogen in abundance on Mars, you would get
extremely excited because it shouldn't be there," Nealson
said.

The reason has to do with the difference between nitrogen
and carbon, the other indispensable organic element.

Unlike carbon, nitrogen is not a major component of rocks
and minerals. This means that any substantial organic
nitrogen deposits found in the soil of Mars, or of another
planet, likely would have resulted from biological activity.

Dimming the hopes of life-on-Mars believers is the makeup
of the planet's atmosphere. The abundant nitrogen in
Earth's atmosphere is constantly replenished through
biological activity. Without the ongoing contribution of living
systems, the atmosphere slowly would lose its nitrogen.

The extremely low nitrogen content in the Martian
atmosphere suggests that biological nitrogen production is
close to zero.

However, the authors write, it is possible that life existed on
Mars at some hypothetical time when nitrogen filled the
atmosphere.

Co-author Douglas Capone, Wrigley Professor of
environmental biology in USC College, said NASA should
establish a nitrogen detection program alongside its water-
seeking effort. He noted that next-generation spacecraft will
have advanced sampling capabilities.

"What we're suggesting here is basically drilling down into
geological strata, which they're going to be doing for water
anyway," Capone said.

"The real smoking gun would be organic nitrogen."

Said Nealson: "If your goal is to search for life, it would be
wise to include nitrogen."

In their acknowledgments, the authors thanked the
students of the Spring 2004 Geobiology & Astrobiology
course at USC, with whom Nealson and Capone began
their discussion on how to search for life outside earth.

"That's really what stimulated this [paper]," Nealson said.

###

The authors also thanked NASA, the Department of Energy
and the National Science Foundation for their financial
support.

Along with Nealson and Capone, USC graduate student
Beverly Flood and former USC Research Professor Radu
Popa (now a professor of biology at Portland State
University) contributed to the Perspectives paper.

Last reviewed:
By John M. Grohol, Psy.D. on
30 Apr 2016
Published on PsychCentral.com. All rights reserved.